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Headlight Control Unit
The headlight control unit only performs functions and supports the acti-
vation of required actuators in the headlight. The necessary data is
provided via CAN or via a direct connection for the headlight control
unit. The headlight control unit is not a "light master" and does not
decide which light is switched "ON". The headlight control unit is
connected to the vehicle electrical system control unit (light master) and
the gateway control unit.
On vehicles with steel springs, the self-levelling sensors are connected
directly to the headlight control unit. The headlight control unit is
powered by the vehicle electrical system.
Headlight Control Unit Software
The two headlight control units in the vehicle work independently. Each
headlight control unit has the individual software and hardware it
requires for calculating the required parameters. During a service,
headlight variant coding must be performed and parameters must be
set using the PIWIS Tester.
The functions, such as automatic range adjustment, static cornering
light and dynamic cornering light, are calculated in the headlight control
unit and implemented by the connected bulbs/actuators. The light
master (vehicle electrical system control unit) issues the command to
switch on the lights.
Dipped Beam
The series reactor (ignition control unit) is integrated in the headlight
control unit for the dipped beam function. The headlight control unit is
hard wired to the vehicle electrical system control unit (light master).
The series reactor (ignition control unit) can also be activated without
the power supply (terminal 15) from the headlight control unit.
Diagnosis is performed when terminal 15 is switched on and when the
lights are activated. The series reactor (ignition control unit) has a power
monitoring and power control system. The headlight control unit sends
its status bit to the CAN bus when dipped beam is "ON". This bit is
monitored by the opposite headlight control unit. If a fault is detected,
emergency mode is enabled and the message "Check dipped beam"
appears on the on-board computer. The same happens if the headlight
control unit intentionally switches off the dipped beam headlight because
of a problem with the automatic range adjustment and dynamic
cornering light functions (message displayed on on-board computer:
"Automatic range adjustment failure" or "Cornering light failure").
Notes
Headlight control units are not installed in
vehicles with halogen headlights. Faults
relating to halogen headlights are detected
by the light master (vehicle electrical system
control unit).
Electrics
Page 9.3
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